1. Field of the Invention
The present invention relates to an industrial robot which is provided with a balancer device which generates a force resisting a load due to gravity.
2. Description of the Related Art
In multiarticulated type industrial robots, there has been known an industrial robot, which is provided with a balancer which generates a force in an opposite direction to the direction of the load due to gravity so as to assist power of a servo motor for driving an arm. For example, Japanese Patent Unexamined Publication No. 10-138189A (JP10-138189A) describes a gas spring type of balancer which uses a compressible gas which is sealed inside of a cylinder so as to apply to a piston rod a repulsive force which corresponds to a change in posture of an arm.
In this regard, this type of balancer is attached in a state where the piston rod is pushed into the cylinder by a predetermined amount, so that even if the arm changes in posture, the piston rod will not reach the stroke end. However, when attaching the balancer, it is difficult to push in the piston rod by a predetermined amount against the gas force of the compressible gas.
On the other hand, there has been known a coil spring type of balancer, which interposes a coil spring inside the cylinder and applies a repulsive force generated by the spring force of the coil spring to a piston rod. For example, in Japanese Patent Examined Publication No. 3142791 (JP3142791B), a through hole is provided in the cylindrical face of a cylinder and a stopper member is protruded inside the cylinder through the through hole. This stopper member is used to hold the coil spring in the compressed state. The balancer is attached in the state with no repulsive force acting on the piston rod. In Japanese Patent Examined Publication No. 3673390 (JP3673390B), an opening part is provided in the end wall of a cylinder, a nut is screwed through the opening part onto an end part of a piston rod which is passed through a retainer, and the coil spring is compressed. The balancer is attached in a state without completely screwing in the nut and in a state where no repulsive force acts on the piston rod.
However, since the balancer described in JP3142791B or JP3673390B provides the cylinder with a through hole or opening part, while it can be applied to a coil spring type of balancer, it cannot be applied to a gas spring type of balancer wherein a compressible gas has to be sealed in.